Cardiovascular hypertension has been induced in rats by dietary administration of the oral contraceptive, Enovid. The projects described here are designed to assess further the use of the rat as an experimental model for the production of hyperytension by means of an oral contraceptive. With this model an attempt will be made to determine: (a) the effect of age on elevation of blood pressure in rats receiving an oral contraceptive; (b) the reversibility of the effect of oral contraceptives on blood pressure; (c) the beta-adrenergic responsiveness of estrogen-treated rats with respect to tail skin temperature, heart rate, water intake, free fatty acid and glucose mobilization and renin secretion; (d) the alpha-adrenergic responsiveness of estrogen-treated rats with respect to vascular reactivity, and (e) the effect of both acute and chronic administration of mestranol and norethynodrel on sodium and potassium exchange in adrenalectomized rats.